1. Field of the Invention
This invention relates to substrates containing a layer of adhesive on at least one surface. More particularly, this invention relates to rigid substrates wherein a layer of adhesive is cohesively bonded to at least one surface of the substrate during a molding operation. This invention also relates to a novel method for preparing these adhesive-coated substrates.
2. Background Information
The process of coating or encapsulating organic and inorganic substrates with molten materials while the substrates are confined in a mold cavity having the contour of the final coated article is described in the patent and journal literature. These materials are non-tacky in the solid state.
Preparing elastomer-coated metal copier rolls by placing the metal core in the central portion of a mold cavity, closing the mold, injecting a liquid curable composition to fill the volume between the perimeter of the core and the wall of the mold cavity and curing the composition to form the elastomer while the roll is enclosed within the mold cavity is described in Japanese Laid Open Application 54/102355. The additional step of pre-coating the metal roll with a primer is described in Japanese Examined Patent Application 89/16657.
Application and bonding of a preformed film to the surface(s) of an injection molded article during the molding operation is described in Netherlands Published Application No. 85/01897; Japanese Laid Open Application 62/253418; U.S. Pat. No. 4,386,042; and Japanese Laid Open Application 56/142045.
The molding of articles containing a metal insert by placing the insert containing a coating of isocyanate-based adhesive combined with a coupling agent in a mold cavity and then injecting into the mold cavity a reactive mixture comprising a polyisocyanate and a polyhydroxylated organic compound is described in Japanese Laid Open Application No. 63/270,107. Encapsulation of metal-containing substrates by a poly(arylene sulfide) is described in U.S. Pat. No. 4,810,590.
Encapsulation of electronic components composed at least in part of a metal by encapsulating the components with a flowable thermosetting resin composition during an injection molding process is described in U.S. Pat. No. 4,327,369.
Japanese Laid Open Application 05/269919 describes a process for coating a metal substrate with a layer of polyethylene that has been graft polymerized with a silane. The steps of the process comprise 1) cleaning the inner and/or outer surface(s) of the metal object by sand-blasting or pickling with HCl, H.sub.2 SO.sub.4 or HNO.sub.3, 2) degreasing the surface(s) using an alkali reagent and 3) coating the object with a molten material by extrusion, injection molding, calendaring or compression molding. A foamed polyurethane or foamed silane-grafted polyethylene layer can be used in place of grafted polyethylene layer.
Molding of a adhesively-bonded sealing material on to a sheet of window glass is described in Japanese Laid Open Application 54/32565.
A method for bonding a layer of silicone rubber to at least a portion of a molded article during a subsequent molding operation is described in Japanese Laid Open Patent Application No. 88/111267. The portion of the article to which the rubber is to be bonded is coated with a primer and the article is placed in a mold with a cavity corresponding to the contour of the coating to be applied. After the mold has been heated to the curing temperature of the silicone rubber composition, the composition is injected into the mold cavity. The coating is simultaneously molded and bonded to the surface of the article.
U.S. Pat. No. 5,002,548, which issued on Jun. 18, 1991, describes a method for coating at least a portion of a marker for identification of animals. The marker is at least partially inserted into a mold with a cavity corresponding in contour to the coated marker. A curable resin is injected into the cavity as the coating material and cured.
Methods taught in the prior art for bonding two substrates along a common interface typically comprise the steps of applying a layer of an adhesive in the form of a liquid or a film to at least one of the surfaces to be bonded, bringing these surfaces into contact with one another and maintaining the surfaces in close contact, preferably under pressure, during solidification and/or curing of the adhesive. The adhesive can be applied by spraying, dipping or placing a preformed layer of the adhesive on one of the surfaces to be bonded.
U.S. Pat. No. 5,160,780 describes a method for bonding a base for an automotive rear view mirror to a glass plate. In accordance with this method, a film of an adhesive composition containing a curable organic polymer or a curable polyorganosiloxane is applied to a glass plate or to one surface of a mirror mounting base formed from a metal or an organic polymer. A laminate consisting of the glass and the mounting base separated by the adhesive layer is formed and the laminate is heated to cure the adhesive.
A shortcoming of laminates prepared by applying a preformed adhesive to one of the substrates to be bonded is the absence of strong cohesive bonding between the adhesive and the substrate to which the adhesive is initially applied.
An objective of this invention is to improve the bonding between a substrate and a layer of adhesive that is applied to at least one surface of the substrate.